Preparation of alkaline earth metals



May 3, 1938. ca. N. KmsEBoM 2,116,245

PREPARATION OF ALKALINE EARTH METALS Filed Sept; 15. 1955 Patented May3, 1938 UNITED ST ATES' PATENT PBEPWTIQN EARTH Gustaf Newton Kirsebom,

land, assignor to Calloy'Limited, land, an English joint- OFFICEClifton, Bristol,-Eng- London, Engstock company Application September13, 1935, Serial No. 40,441

In Great Britain September 21, 1934 6' Claims. (CI. 75-07) Thisinvention is for improvements in or relating to the preparation ofmagnesium.

According to the present invention magnesium is prepared by heating analloy thereof in a closed ves'selto a temperature above thevolatilization temperature of magnesium and condensing the metal vapourgiven oil.

In its simplest form the invention consists in volatilizing themagnesium in a closed vessel from 1a previously prepared alloy thereofwith alumin- At the temperature required, e g. 1200-1300 C. for carryingout the process of the invention,

I aluminium has an extremely destructive efiect upon any of therefractory crucibles or furnace linings employed. If, for example, thealuminium containing the alkaline earth material were simply heatedexternally in a crucible, the heavy costs entailed-through thedisintegration of the crucible may make the process uncommercial.

It is therefore of great importance in carrying out the process oi theinvention to employ a method of heating, in which the heat isdevelopedwithin the body of the metal itself and the crucible onlybecomes heated by conduction from,the hot metal.

. vOne very convenient way in which the inven- Q tion maybe carried intoeffect is to heat the magnesium al inium alloy in a high frequencyelectric furnace lined with carbon or other suitable lining material.

For example; in carrying out the process, an

aluminiummagnesium alloy may conveniently be prepared by the processdescribedinUnited States ,Patent dated 14th November 1933 No. 1,935,245and such alloy may then be heated in a high frequency furnace withoutseparatingthe alloy from the dross consisting of particles of alloydispersed in aluminium oxide which is.

It is not, however; necessary to ,prepare an aluminium alloy previously.On the contrary,f metallic aluminium may be melted in a crucible I withcalcined magnesite or material containing magnesium oxide in pieces ofsuflicientsize to overcome the surface tension of, the molten aluminiumat a temperature above the volatiliza-' ,tion point of the saidyalkalineearth metal. The aluminium will then reduce the magnesium oxide formedin the reduction process.

. tion temperature of magnesium.

. The process of the invention has the great ad- 15 vantagethat nohydrogen is required to prevent a reverse reaction and no special meansare required for evacuating the apparatus before or during the reaction.The small amount of air which is initially contained in the closedchamber 20 in which the reaction is carried out reacts in.the earlystages of the process with the first magnesium formed, producing a.small amount of oxide and nitride dust which does not interfere with thesubsequent condensation of metal.

In carrying out the distillation the condensing 25 tube may be immersedin an oil bath and the condensed magnesium drops into this oil bath inlarge pieces, which after cleaning, inay easily melted together, e. g.under a flip: or by other means.

As the vapour pressure, of aluminium at these temperatures ispractically nil, magnesium condensed in this way does not even containtraces of (aluminium and is.chemically pure in other I respects. I I

It has sometimes been found useful to charge,

- the crucible first with the calcined magnesite in and the magnesiumformedalloys with the alus minium and simultaneously the magnesium willbe volatilized and may be condensed in a suitable chamber. In thiswaythe reaction may be continueduntil' the bulk of the aluminium hasbeen converted to oxide.

,the disc and the sides of the crucible.

pieces and tocover the charge with a disc, preferablyv of graphite, ofsomewhat smaller diameter than the crucible to allow space for moltenmetal to trickle down between the periphery of Moltenaluminium oraluminium magnesium alloy is then poured in: The weight of the discprevents the calcinedmagnesite from floating up to the surface of themolten aluminium and in this way from the start'of the reaction themagnesite.is surrounded by aluminium ensuring thereby a quicker and morethorough reaction between the pieces ofmagnesite and aluminium. Afterfinishing distillation the still molten (residual metal isremoved fromthe dross by tilting the crucible with the disc in place.

Instead of using pieces of calcined magnesite,

2 I briquettes of calcined magnesite and carbon may be employed.

The reaction between the calcined magnesite and aluminium will thenfirst take place and the briquettes will retain their form but willmainly consist of aluminium, aluminium carbide and aluminium oxide whichmay be worked up to aluminium. It is also possible instead of carbon touse other materials capable of forming briquettes with magnesite.

In the practical working of the process for the manufacture of magnesiumit has been found that magnesium does not suihciently readily distil outof an alloy containing less than 8 per cent magnesium. The distillationmay therefore be conveniently carried out in 'such a way that 8 vpercent aluminium-magnesium-alloy is used as starting material along withcalcined magnesite, for example, in equal parts by weight. The magnesiumwill distil of! and this will go on until practically all the magnesiumin the magnesite over and above what is required to maintain an 8 percent alloy will distil over. when the rate of distillation slackens off,the remaining alloy will contain 8 per cent magnesium approximately.

By working with a'series of furnaces it is, therefore, possible onthe'hrge scale to use the 8 per cent aluminium-magnesium-alloy left overfrom one furnace by pouring it into the next furnace along with thenecessary fresh aluminium and calcined magnesite in lumps or pieces.

The system is then closed and distillation resumed until the rate ofdistillation again slackens off when the molten metal remaining in'thefurnace and consisting of an aluminium-magneslum-alloy of approximately8' per cent will be transferred to the next furnace in the series and soon. After the removal of the 8 per cent aluminium-magnesium-alloy fromany furnace, the dross will be removed and treated separately for therecovery of aluminium, the furnace then being ready for a new operation.

In carrying out the process on a commercial scale it is not practicableto conduct the condensed magnesium directly into an oil bath owing tothe amount of oil volatilized and the danger of explosion, but providedair is kept out of the apparatus during the volatilization stage, it ispossible to collect the condensed metal without any serious losses in achamber.

An arrangement of apparatus which has been found to work satisfactorilyin practice is represented by the accompanying drawing in which Fig. 1shows diagrammatically the arrangement of thewhole apparatus and Fig. 2shows a modified form of oil seal.

Referring to Fig.1 an ordinary injector furnace iris heated by an oiljet 2. In the furnace a graphite crucible l is placed which is longenough to protrude above the top of the furnace.

The crucible is covered by a graphite lid 4. In

the side of the crucible above the level of the top of the furnace, anopening 0 is made to which the condenser pipe 'I is attached by thegraphite and fireclay luting 5. The condenser pipe 1 leads into the topof a hood 8 standing in a shallow bath of oil la. Inside .the hood is acylindrical receiver 9 in'two parts held't'ogether bythe tray l0 and thering II. The receiver I stands upon a ring ii to raise it inside thehood. In the side of the hood a narrow tube H is fixed with its centreline in alignment with the centre of the condenser tube 1 and extendingoutwa'rdfrom the hood in a planev parallel with that of the condensertube I. The

above the level of the 011 end of this tube is a packing gland I!through which a rod I! passes and extends along to the bend in thecondenser pipe I. This rod is sealed with an oil seal at its lower end.In this pipe l4 there is also provided a narrow inlet pipe 16 ,which maybe closed with a valve or rubber tube and clip.

In operation, magnesium oxide-containing material e. g. burnt magnesiteis placed in the crucible 3 and molten aluminium filled into thecrucible about half way. The system is then closed and the crucibleheated to a temperature of 1200-1300 C.

The magnesium oxide is reduced and at the temperature of reduction it isvolatilized off and condensed in the condenser tube 1. The condensertube becomes heated by the heat of condensation to a temperature abovethe melting point of magnesium and the metal then melts and runs downdropping into the receiver 9. From time to time the rod I5 is moved tomake sure that there has been no building up of condensed magnesium inthe condenser tube 1 which may cause a blockage in the system. At theend of the run the furnace is shut down and as it cools, a reducedpressure is created in the hood I. Enough air is allowed to enterthrough the inlet IE to avoid oil being sucked up into the I When themetal in .the receiver has cooled sufficiently the hood is removed andthe tray III and the ring II are knocked off the receiver 9 which isthen broken apart.

Instead of the-oil tray the hood is closed with a disc 20 which isclamped to the bottom of the hood 8 by means of wedges 23 passingthrough eye-pieces 2| which latter are welded on to the through slots inthe periphery of the disc 20. The hood I in this case is provided with aside tube It bent in the form of a U and dipping down into a small oilbath it.

While the apparatus above described employs an oil fired furnace, it is,of course, preferable to employ a high frequency furnace for the reasonsalready set out.

The metal obtainedas 'above described con- II, a slightly modifiedformof oil lock is shown in Fig. 2. In this case sides of the hood 8 andpass sists of large globules and prills separated by films of magnesiumoxide and nitride. By simple melting under a flux such as carnallite asolid ingot of high purity may be produced.

I claim:'-

1. A process for preparing metallic magnesium which comprises heatingmagnesium oxide at a temperature above the boiling point of magnesiumwith an aluminium-magnesium alloy containing about 8% of magnesium andcondensing the metal vapour given off.

2. A process for preparing metallic magnesium which comprises heatingtogether magnesium oxide with excess of aluminium by first chargingpieces of magnesium oxide into a crucible and covering the said; pieceswith a loosely fitting graphite cover and pouring molten aluminium intothe crucible and'thereafter heating the molten aluminium and magnesiumoxide above the volatilization temperature of magnesium.

3. A process as claimed in claim '2 wherein there is employedinstead ofpieces 01' magnesium aluminium in a closed vessel above the boilingpoint of but below that of aluminium, the magnesium oxide being inpieces of suiflcient size to overcome the surface tension of the moltenaluminium and the amount or aluminium belngsuflicient to form an alloywith the reduced magnesium; (b) condensing the magnesium vapour formed.

15 the reduction process is carried out at a temperature Just above theboiling point pi magnesium 6. A process for preparing metallic magnesiumwhich comprises forming an alloy of magnesi with aluminium by heatingtogether magnesi oxide with excess of aluminium at a temperature abovethe boiling point oi magnesium whereby volatilization is effectedsimultaneously with the regeneration of the aluminium-magnesium alloy,and'heating the aluminium-magnesium alloy in a closed vessel to atemperature above the boiling point of magnesium and condensing themetal a vapour given ofl. I 5. A process as claimed in claim 4 whereinops'rsr' zmsmaom;

